U.S. patent number 7,564,008 [Application Number 11/295,150] was granted by the patent office on 2009-07-21 for alumina member and manufacturing method thereof.
This patent grant is currently assigned to NGK Insulators, Ltd.. Invention is credited to Hiroto Matsuda, Yutaka Mori, Kazuhiro Nobori.
United States Patent |
7,564,008 |
Mori , et al. |
July 21, 2009 |
Alumina member and manufacturing method thereof
Abstract
An electrostatic chuck includes a base of a sintered body
containing alumina, an electrode as a power-supplied member
embedded in the base and supplied with electric power, a bonding
member embedded in the base and bonded to the electrode, in which a
difference in coefficient of thermal expansion from the sintered
body is 2.times.10.sup.-6/K or less, and a melting point is higher
than baking temperature of the sintered body, and a terminal bonded
to the electrode through the bonding member.
Inventors: |
Mori; Yutaka (Nagoya,
JP), Matsuda; Hiroto (Ogaki, JP), Nobori;
Kazuhiro (Handa, JP) |
Assignee: |
NGK Insulators, Ltd.
(Nagoya-shi, JP)
|
Family
ID: |
35966004 |
Appl.
No.: |
11/295,150 |
Filed: |
December 6, 2005 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20060169688 A1 |
Aug 3, 2006 |
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Foreign Application Priority Data
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Dec 14, 2004 [JP] |
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P2004-361882 |
Sep 5, 2005 [JP] |
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P2005-256484 |
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Current U.S.
Class: |
219/444.1;
118/724 |
Current CPC
Class: |
B23K
35/24 (20130101); H01L 21/68757 (20130101); C04B
37/026 (20130101); C04B 37/025 (20130101); C04B
35/645 (20130101); H01L 21/67103 (20130101); B23K
35/32 (20130101); H01L 21/6833 (20130101); C04B
2237/76 (20130101); C04B 2237/84 (20130101); C04B
2237/72 (20130101); Y10T 29/49087 (20150115); C04B
2237/704 (20130101); C04B 2237/125 (20130101); C04B
2235/6562 (20130101); C04B 2237/122 (20130101); C04B
2235/658 (20130101); C04B 2237/123 (20130101); C04B
2237/403 (20130101); C04B 2237/086 (20130101); C04B
2237/343 (20130101); C04B 2235/6567 (20130101); C04B
2237/706 (20130101); C04B 2237/62 (20130101) |
Current International
Class: |
H05B
3/68 (20060101); C23C 16/00 (20060101) |
Field of
Search: |
;219/444.1,541-548
;118/724,725 ;339/306-314 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0 886 312 |
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Dec 1998 |
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EP |
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1 249 433 |
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Oct 2002 |
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EP |
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697 306 |
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Sep 1953 |
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GB |
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09-008114 |
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Jan 1997 |
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JP |
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11-012053 |
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Jan 1999 |
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JP |
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1999-006874 |
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Jan 1999 |
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KR |
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01/43183 |
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Jun 2001 |
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WO |
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Other References
Intrater, J., "The Challenge of Bonding Metals to Ceramics,"
Machine Design, Penton Media, Cleveland, OH, vol. 61, No. 24, Nov.
23, 1989, pp. 95-100. cited by other.
|
Primary Examiner: Paik; Sang Y
Attorney, Agent or Firm: Burr & Brown
Claims
What is claimed is:
1. An alumina member, comprising: a base of a sintered body
containing alumina; a power-supplied member embedded in the base
and supplied with electric power, said power-supplied member being
at least one of an electrode and a resistance heating element; a
bonding member embedded in the base and bonded to the
power-supplied member by hot-pressing, said bonding member having
the shape of a disc or a ball and comprising niobium; a terminal
bonded to the power-supplied member through the bonding member,
wherein a difference in coefficient of thermal expansion between
the bonding member and the sintered body is 2.times.10.sup.-6/K or
less, a melting point of the bonding member is higher than a baking
temperature of the sintered body, and a portion of the base
positioned below the power-supplied member and at a periphery of
the bonding member contains 1.4-1.5 wt % carbon.
2. The alumina member according to claim 1, wherein a tensile
strength of the base at a breaking point thereof is 1.0 kg
weight/mm.sup.2 or more when a load to pull the base and the
terminal in directions separating from each other is applied
thereto.
3. The alumina member according to claim 1, wherein a punching load
to the base at the breaking point thereof is 30 kg weight or more
when a load is applied thereto in a direction from the terminal
toward the bonding member.
4. The alumina member according to claim 1, wherein the bonding
member and the terminal are bonded to each other by at least one of
indium, gold, silver, an aluminum-alumina composite material, and a
gold-nickel alloy.
5. A method of manufacturing an alumina member, comprising the
steps of: preparing a compact comprising alumina, a carbon source,
a power-supplied member and a bonding member, the carbon source
being arranged below the power-supplied member and at a periphery
of the bonding member; and hot pressing the compact to integrate
the alumina, power-supplied member and bonding member to one
another to form a sintered body, wherein an amount of the carbon
source and conditions of the hot-pressing are selected such that
1.4-1.5 wt % carbon is present in the sintered body below the
power-supplied member and at the periphery of the bonding member,
wherein a difference in coefficient of thermal expansion between
the bonding member and the sintered body is 2.times.10.sup.-6/K or
less, and wherein a melting point of the bonding member is higher
than a temperature of the hot pressing step.
6. The method of manufacturing an alumina member according to claim
5, wherein the bonding member is coated with carbon or a carbon
source.
7. The method of manufacturing an alumina member according to claim
5, wherein the bonding member comprises niobium.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority
from prior Japanese Patent Application No. P2004-361882, filed on
Dec. 14, 2004, and No. P2005-256484, filed on Sep. 5, 2005; the
entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an alumina member suitable for an
electrostatic chuck and a heater and to a manufacturing method
thereof.
2. Description of the Related Art
Heretofore, in a semiconductor manufacturing process, there has
been used an alumina member, such as an electrostatic chuck in
which an electrode is embedded in an alumina sintered body, and a
heater in which a resistance heating element is embedded in such an
alumina sintered body. To each the electrode and the resistance
heating element, a terminal for connecting a power supply line
thereto is bonded by brazing or the like. Moreover, in the alumina
sintered body, a hole for inserting the terminal thereinto is
formed (for example, refer to Japanese Patent Laid-Open Publication
No. H11-12053 (published in 1999)).
However, the conventional alumina member has had a subject that the
terminal and a power-supplied member to be supplied with electric
power, such as the electrode and the resistance heating element,
are desired to be bonded to each other more firmly. Moreover, there
has been a possibility that the formation of the hole, and so on,
may bring a strength reduction of the alumina member. In
particular, in the case of a Coulomb-type electrostatic chuck,
since thickness of a dielectric layer thereof is thin, there has
been a possibility that the strength reduction may be brought.
SUMMARY OF THE INVENTION
In this connection, it is an object of the present invention to
provide a strong alumina member in which a power-supplied member
and a terminal are firmly bonded to each other, and to provide a
manufacturing method thereof.
An alumina member according to the present invention includes: a
base of a sintered body containing alumina; a power-supplied member
embedded in the base and supplied with electric power; a bonding
member embedded in the base and bonded to the power-supplied
member, in which a difference in coefficient of thermal expansion
from the sintered body is 2.times.10.sup.-6/K or less, and a
melting point is higher than baking temperature of the sintered
body; and a terminal bonded to the power-supplied member through
the bonding member.
According to the alumina member as described above, the
power-supplied member and the terminal are firmly bonded to each
other. Moreover, the base of the sintered body containing alumina
and the bonding member are approximate to each other in coefficient
of thermal expansion. Accordingly, a crack which may be caused by
embedding the bonding member in the base can be prevented from
occurring. Therefore, strength of the alumina member can be
enhanced by embedding the bonding member therein, and the crack
which may be caused by the embedding can also be prevented from
occurring. Hence, the strength of the alumina member can be
enhanced. In addition, the melting point of the bonding member is
higher than the baking temperature of the sintered body, and
accordingly, in a manufacturing process of the alumina member, the
bonding member can be prevented from being deformed, and a
component of the bonding member can be prevented from being
diffused into the base. Hence, a malfunction does not occur owing
to the embedding of the bonding member.
It is preferable that the bonding member contain at least either
niobium (Nb) or platinum (Pt). According to this, the
power-supplied member and the terminal can be bonded to each other
more firmly. In addition, the base composed of the sintered body
containing alumina and the bonding member can be approximated to
each other in coefficient of thermal expansion. Accordingly, the
crack of the base can be further prevented from occurring, and the
strength of the alumina member can be further enhanced. Moreover,
when the bonding member contains platinum, the component of the
bonding member can be prevented from being diffused into the
base.
It is preferable that at least a part of the sintered body of the
base contain 0.05 to 0.5 wt % carbon. According to this, the
strength of the base can be enhanced, and the strength of the
alumina member can be further enhanced.
It is preferable that the power-supplied member be at least one of
either an electrode or a resistance heating element. According to
this, the alumina member can be used as an electrostatic chuck in
which the electrode is embedded and a heater in which the
resistance heating element is embedded.
It is preferable that the bonding member be disc-like or ball-like.
According to this, the crack can be further prevented from
occurring, and the strength of the alumina member can be further
enhanced.
It is preferable that tensile strength of the base at a breaking
point thereof be 1.0 kg weight/mm.sup.2 or more when a load to pull
the base and the terminal in reverse directions is applied thereto.
According to this, the power-supplied member and the terminal can
be bonded to each other more firmly.
It is preferable that a load (hereinafter, referred to as a
"punching load") to the base at the breaking point thereof be 30 kg
weight or more when a load is applied thereto in a direction from
the terminal toward the bonding member. According to this, strength
of the base in the periphery of the power-supplied member and the
terminal can be increased, and the strength of the alumina member
can be maintained high.
It is preferable that the bonding member and the terminal be bonded
to each other by any of indium, gold, silver, an aluminum-alumina
composite material, and a gold-nickel alloy. According to this, the
bonding member and the terminal are firmly bonded to each other,
and the bonding of the power-supplied member and the terminal,
which are bonded to each other through the bonding member, can be
made firmer.
It is preferable that the power-supplied member and the bonding
member be bonded to each other by hot pressing. According to this,
the power-supplied member and the bonding member are firmly bonded
to each other, and the bonding of the power-supplied member and the
terminal, which are bonded to each other through the bonding
member, can be made firmer.
A method of manufacturing an alumina member according to the
present invention includes the steps of: fabricating a base
composed of a sintered body containing alumina, in which a power
supplied member and a bonding member bonded to the power-supplied
member are embedded, the bonding member having a difference in
coefficient of thermal expansion from the sintered body of
2.times.10.sup.-6/K or less, and a melting point higher than baking
temperature of the sintered body; and bonding a terminal to the
bonding member. According to this, a strong alumina member in which
the power-supplied member and the terminal are firmly bonded to
each other through the bonding member can be provided.
It is preferable that a compact containing alumina, the
power-supplied member, and the bonding member be integrally baked
by hot pressing. According to this, the power-supplied member and
the bonding member can be firmly bonded to each other, and the
bonding of the power-supplied member and the terminal, which are
bonded to each other through the bonding member, can be made
firmer. In addition, in the manufacturing process, the bonding
member can be prevented from being deformed, and the component of
the bonding member can be prevented from being diffused into the
base.
In this case, it is preferable that the compact, the power-supplied
member, and the bonding member be baked in a state where carbon is
present in the periphery of the bonding member. According to this,
the component of the bonding member can be further prevented from
being diffused into the base.
For example, at least a part of the compact contains at least one
of either carbon powder or a binder serving as a carbon source,
thus making it possible to perform the baking in the state where
carbon is present in the periphery of the bonding member.
In this case, it is preferable that a content and baking condition
of at least one of either the carbon powder or the binder in the
compact be adjusted so that carbon contained in at least a part of
the sintered body of the base can be 0.05 to 0.5 wt %. According to
this, a stronger alumina member can be provided.
Moreover, also by coating the bonding member with carbon or the
carbon source, the baking can be performed in the state where
carbon is present in the periphery of the bonding member.
According to the present invention, the strong alumina member in
which the power-supplied member and the terminal are firmly bonded
to each other, and the manufacturing method thereof, can be
provided.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A is a cross-sectional view of an electrostatic chuck
according to an embodiment of the present invention, taken along a
line IA-IA of FIG. 1B, and FIG. 1B is a plan view of the
electrostatic chuck according to the embodiment of the present
invention.
FIG. 2A is a cross-sectional view of a heater according to the
embodiment of the present invention, taken along a line IIA-IIA of
FIG. 2B, and FIG. 2B is a plan view of the heater according to the
embodiment of the present invention.
FIG. 3 is across-sectional view of an electrostatic chuck
subjectable to a heat treatment according to the embodiment of the
present invention.
FIG. 4 is a schematic view showing a measurement method of tensile
strength.
FIG. 5 is a schematic view showing a measurement method of a
punching load.
DETAILED DESCRIPTION OF THE EMBODIMENTS
FIG. 1 shows an electrostatic chuck 10 as an alumina member. FIG.
1A is a cross-sectional view of the electrostatic chuck 10, and
FIG. 1B is a plan view thereof. The electrostatic chuck 10 includes
a base 11, an electrode 12, a bonding member 13, and a terminal 14.
The electrostatic chuck 10 is a Coulomb-type electrostatic
chuck.
FIG. 2 shows a heater 20 as the alumina member. FIG. 2A is a
cross-sectional view of the heater 20, and FIG. 2B is a plan view
thereof. The heater 20 includes a base 21, a resistance heating
element 22, a bonding member 23, and terminals 24.
FIG. 3 shows an electrostatic chuck 30 subjectable to a heat
treatment, as the alumina member. The electrostatic chuck 30
includes a base 31, an electrode 12, a resistance heating element
22, bonding members 13 and 23, and terminals 14 and 24. The
electrostatic chuck 30 combines a function of the electrostatic
chuck 10 shown in FIG. 1 and a function of the heater 20 shown in
FIG. 2.
The bases 11, 21 and 31 are sintered bodies containing alumina.
Each of the bases 11, 21 and 31 can be composed of an alumina
sintered body, a sintered body containing alumina and zirconia
(ZrO.sub.2), a sintered body containing alumina and magnesia (MgO),
or the like. It is preferable that each of the bases 11, 21 and 31
be composed of the alumina sintered body.
It is preferable that purity of alumina of the sintered body
composing each of the bases 11, 21 and 31 be 99.5 wt % or more.
According to this, strength of each of the bases 11, 21 and 31 can
be enhanced, and corrosion resistance thereof can also be enhanced.
In addition, contamination of a substrate can be prevented. It is
more preferable that the purity of alumina of the sintered body
composing each of the bases 11, 21 and 31 be 99.7 wt % or more.
Although a shape of each of the bases 11, 21 and 31 is not limited,
for example, each of the bases 11, 21 and 31 can be formed into a
circular or polygonal plate-like body when viewed from the
above.
It is preferable that at least a part of the sintered body of each
of the bases 11, 21 and 31 contain 0.05 to 0.5 wt % carbon.
According to this, the strengths of the bases 11, 21 and 31 can be
enhanced, and strengths of the electrostatic chucks 10 and 30 and
the heater 20 can be further enhanced.
It is preferable that a density of the sintered body composing each
of the bases 11, 21 and 31 be 3.80 to 4.00 g/cm.sup.3. According to
this, the strength of each of the bases 11, 21 and 31 can be
enhanced, and the corrosion resistance thereof can also be
enhanced. It is more preferable that the density of the sintered
body composing each of the bases 11, 21 and 31 be 3.93 to 4.00
g/cm.sup.3.
It is preferable that an open void content of the sintered body
composing each of the bases 11, 21 and 31 be 0%. Moreover, it is
preferable that the maximum void diameter of the sintered body
composing each of the bases 11, 21 and 31 be 100 .mu.m or less.
According to these, withstand voltages of the bases 11, 21 and 31
can be made large. Hence, arcing can be prevented from occurring.
It is more preferable that the maximum void diameter of the
sintered body be 50 .mu.m or less.
Moreover, it is preferable that four-point bending strength (JIS
R1601) of the sintered body composing each of the bases 11, 21 and
31 at room temperature be 300 MPa. It is more preferable that the
four-point bending strength of the sintered body composing each of
the bases 11, 21 and 31 be 350 MPa or more, and it is further
preferable that the four-point bending strength be 365 MPa or more.
Moreover, when the sintered body composing each of the bases 11, 21
and 31 contains 0.05 to 0.5 wt % carbon, it is preferable that the
four-point bending strength of the sintered body composing each of
the bases 11, 21 and 31 be 500 MPa or more.
The bases 11, 21 and 31 have substrate mounting surfaces 16, 26 and
36, respectively. On the substrate mounting surfaces 16, 26 and 36,
the substrates such as semiconductor wafers and liquid crystal
substrates are mounted. It is preferable that a center line average
roughness (Ra) (JIS B0601) of each of the substrate mounting
surfaces 16, 26 and 36 be 0.5 .mu.m or less. According to this,
particles can be prevented from occurring. Moreover, in the case of
flowing backside gas between a back surface of the substrate and
each of the substrate mounting surfaces 16, 26 and 36, a flow of
the backside gas can be prevented from being disturbed, and
temperature of the substrate can be maintained even. It is more
preferable that the center line average roughness (Ra) of each of
the substrate mounting surfaces 16, 26 and 36 be 0.1 to 0.5 .mu.m.
According to this, processing cost of the bases 11, 21 and 31 can
be reduced.
Moreover, each of the bases 11 and 31 of the electrostatic chucks
10 and 30 includes a dielectric layer 11a. It is preferable that
thickness of the dielectric layer 11a be 0.05 to 0.5 mm. According
to this, absorbing powers of the electrostatic chucks 10 and 30 can
be enhanced. It is more preferable that the thickness of the
dielectric layer 11a be 0.05 to 0.4 mm.
It is preferable that a degree of flatness of the dielectric layer
11a, that is, a difference between the maximum value and minimum
value of a distance from the electrode 12 to each of the substrate
mounting surfaces 16 and 36, be 0.2 mm or less. According to this,
even absorbing powers of the electrostatic chucks 10 and 30 can be
obtained. It is more preferable that the degree of flatness be 0.1
mm or less.
Moreover, it is preferable that volume resistivity (JIS C2141) of
the dielectric layer 11a at room temperature be 1.times.10.sup.15
Ocm or more. It is more preferable that the volume resistivity of
the dielectric layer 11a be 1.times.10.sup.16 Ocm or more. It is
further preferable that the volume resistivity of the dielectric
layer 11a be 1.times.10.sup.17 Ocm or more. According to these,
high absorbing power of each of the electrostatic chucks 10 and 30
and good responsiveness thereof to attaching/detaching of the
substrate can be obtained.
Furthermore, when at least a part of the sintered body of each of
the bases 11 and 31 contains carbon, it is preferable that the
dielectric layer 11a in each of the bases 11 and 31 should not
contain carbon. In each of the bases 11 and 31, a portion other
than the dielectric layer 11a, that is, the sintered body composing
a layer under the electrode 12, may contain carbon, or not.
It is preferable that a withstand voltage (JIS C2141) of the
sintered body composing each of the bases 11 and 31 of the
electrostatic chucks 10 and 30 be 15 kV/mm or more. It is more
preferable that the withstand voltage of the sintered body
composing each of the bases 11 and 31 be 18 kV/mm or more.
According to this, the arcing can be prevented from occurring.
The bases 11, 21 and 31 have holes 15 and 25 for inserting the
terminals 14 and 24 thereinto. The holes 15 and 25 extend from back
surfaces 17, 27 and 37 (opposite surfaces to the substrate mounting
surfaces 16, 26 and 36) of the bases 11, 21 and 31 to the bonding
members 13 and 23. Accordingly, partial portions (regions facing to
the holes 15 and 25) of the bonding members 13 and 23 are exposed.
The base 21 has two holes 25 for inserting two terminals 24
thereinto. The base 31 has three holes 15 and 25 for inserting
three terminals 14 and 24 thereinto.
The electrodes 12 and the resistance heating elements 22 are
embedded in the bases 11, 21 and 31. The electrodes 12 and the
resistance heating elements 22 are power-supplied members to be
supplied with electric power. For the power-supplied members, for
example, a high melting point conductive material can be used.
Specifically, as the power-supplied members, there can be used high
melting point metal such as tungsten (W), niobium (Nb), and
molybdenum, an alloy thereof, and a compound of high melting point
metal such as tungsten carbide (WC).
Each of the electrodes 12 generates the absorbing power by being
supplied with the electric power. For the electrode 12, for
example, a printed electrode on which a print paste containing high
melting point conductive material powder is printed in a mesh
shape, a comb shape, a circular shape, or the like can be used. In
this case, it is preferable that the electrode 12 be formed by
using a print paste in which alumina powder is mixed into the high
melting point conductive material powder. According to this; the
electrode 12 can be firmly bonded to each of the bases 11 and 31.
Moreover, for the electrode 12, a mesh-like bulk member (wire
netting) of the high melting point conductive material, a bulk
member (punching metal) of the high melting point conductive
material, into which a large number of holes is drilled, and the
like can be used.
Each of the resistance heating elements 22 generates heat by being
supplied with the electric power. For the resistance heating
element 22, a printed heating element on which the print paste
containing the high melting point conductive material powder is
printed in a spiral shape, a mesh shape, a shape folded plural
times, and the like, can be used. In this case, it is preferable
that the resistance heating element 22 be formed by using the print
paste in which the alumina powder is mixed into the high melting
point conductive material powder. According to this, the resistance
heating element 22 can be firmly bonded to each of the bases 11 and
31. Moreover, for the resistance heating element 22, a coil-like or
linear bulk member of the high melting point conductive material,
and the mesh-like bulk member (wire netting) of the high melting
point conductive material, can be used.
The bonding member 13 is embedded in each of the bases 11 and 31.
The electrode 12 as the power-supplied member and the terminal 14
are bonded to each other through the bonding member 13. The bonding
members 23 are embedded in the bases 21 and 31. Moreover, the
resistance heating elements 22 as the power-supplied members and
the terminals 24 are bonded to each other through the bonding
members 23.
A difference between a coefficient of thermal expansion (CTE) of
each of the bonding members 13 and 23 and a coefficient of thermal
expansion of the alumina-containing sintered body composing each of
the bases 11, 21 and 31 is 2.times.10.sup.-6/K or less. According
to this, the different in coefficient of thermal expansion between
each of the bases 11, 21 and 31 of the alumina-containing sintered
bodies and each of the bonding members 13 and 23 is small, and
accordingly, cracks which may be caused by embedding the bonding
members 13 and 23 into the bases 11, 21 and 31 can be prevented
from occurring. Therefore, the strengths of the alumina members 10
and 30 and the heater 20 can be maintained high. Moreover, the
arcing can also be prevented from occurring. It is more preferable
that the difference in coefficient of thermal expansion between
each sintered body of the bonding members 13 and 23 and each of the
bases 11, 21 and 31 be 1.5.times.10.sup.-6/K or less.
Each melting point of the bonding members 13 and 23 is higher than
baking temperature of the sintered body composing each of the bases
11, 21 and 31. According to this, even if the bonding members 13
and 23 are maintained at the baking temperature in a manufacturing
process of the alumina member such as the electrostatic chucks 10
and 30 and the heater 20, the bonding members 13 and 23 can be
prevented from being deformed, and a component of the bonding
members can be prevented from being diffused into the bases 11, 21
and 31. Hence, a malfunction does not occur owing to the embedding
of the bonding members 13 and 23. It is preferable that each
melting point of the bonding members 13 and 23 be higher than the
baking temperature of the sintered body by 50.degree. C. or
more.
It is preferable that the bonding members 13 and 23 contain at
least one of either niobium (Nb) or platinum (Pt). According to
this, the terminals 14 and 24 can be bonded to the electrodes 12
and the resistance heating elements 22, which are the
power-supplied members, more firmly. In addition, the bases 11, 21
and 31 composed of the alumina-containing sintered bodies and the
bonding members 13 and 23 can be approximated to each other in
coefficient of thermal expansion. Accordingly, the cracks which may
be caused by embedding the bonding members 13 and 23 in the bases
11, 21 and 31 can be further prevented from occurring. Moreover,
the arcing can also be prevented. Furthermore, when the bonding
members 13 and 23 contain platinum, the component of the bonding
members can be prevented from being diffused into the bases 11, 21
and 31 by a heat treatment such as baking in the manufacturing
process of the alumina member. Furthermore, the melting point of
niobium is 2470.degree. C., and the melting point of platinum is
1770.degree. C. The baking temperature of the alumina-containing
sintered body can be selected, for example, from a range of 1500 to
1700.degree. C. Hence, each melting point of the bonding members 13
and 23 can be set higher than the baking temperature by 50.degree.
C. or more.
For example, as the bonding members 13 and 23, there can be used
niobium, alloys of niobium and various metals, platinum, alloys of
platinum and various metals, and the like. It is preferable that
the bonding members 13 and 23 be composed of niobium or platinum.
In the case of using the alloys as the bonding members 13 and 23,
it is preferable that a content of niobium or platinum be 50 vol %
or more.
The shapes of the bonding members 13 and 23 are not limited. For
example, the bonding members 13 can be formed into a disc shape
(columnar shape), and the bonding members 23 can be formed into a
ball shape. According to these, the cracks can be further prevented
from occurring between the bonding members 13 and 23 and the bases
11, 21 and 31, and the strengths of the electrostatic chucks 10 and
30 and the heater 20 can be further enhanced. Moreover, the arcing
can also be prevented from occurring.
It is preferable that thickness (vertical height in FIG. 1) of each
disc-like bonding member 13 be 0.2 to 1.0 mm. It is preferable that
diameter of the bonding member 13 be 0.5 to 4.0 mm. It is more
preferable that the thickness of the bonding member 13 be 0.5 to
1.0 mm, and it is more preferable that the diameter thereof be 0.5
to 3.0 mm. It is preferable that diameter of the ball-like bonding
member 23 be 2.0 to 6.0 mm. It is more preferable that the diameter
of the bonding member 23 be 3.0 to 5.0 mm. The shapes of the
bonding members 13 and 23 may also be oval and the like.
For example, as shown in FIG. 1A and FIG. 3, each bonding member 13
is provided in contact with the power-supplied member such as the
electrode 12, and is bonded to the power-supplied member by being
heated and pressurized, for example, by hot pressing. Moreover, as
shown in FIG. 2A and FIG. 3, each bonding member 23 can have a
through hole 23a. An end of the power-supplied member such as the
coil-like resistance heating element 22 is inserted into the
through hole 23a, the bonding member 23 and the power-supplied
member are heated and pressurized, for example, by the hot
pressing, and the bonding member 23 is thus bonded to the
power-supplied member. In particular, it is preferable that the
bonding members 13 and 23 be bonded to the power-supplied members
such as the electrodes 12 and the resistance heating elements 22 by
thermal pressure bonding according to the hot pressing. According
to this, the bonding members 13 and 23 are firmly bonded to the
electrodes 12 and the resistance heating elements 22, and the
bonding of the terminals 14 and 24 to the electrodes 12 and the
resistance heating elements 22, the bonding being formed through
the bonding members 13 and 23, can be made firmer.
The terminals 14 are bonded to the electrodes 12 through the
bonding members 13. To the terminals 14, power supply lines for
supplying the electric power to the electrodes 12 are connected.
The terminals 24 are bonded to the resistance heating elements 22
through the bonding members 23. To the terminals 24, power supply
lines for supplying the electric power to the resistance heating
elements 22 are connected. The terminals 14 and 24 are inserted
into the holes 15 and 25 drilled in the bases 11, 21 and 31, and
are bonded to the exposed portions of the bonding members 13 and
23. The terminals 14 and 24 can be composed of molybdenum and
niobium. Surfaces of the terminals 14 and 24 may also be coated
with gold (Au) and nickel (Ni).
The bonding members 13 and 23 and the terminals 14 and 24 can be
bonded to each other, for example, by brazing. A metal brazing
material, a composite brazing material as a composite material of
metal and ceramics, and the like, can be used as the brazing
material. For example, as the brazing material, there can be used
indium (In), gold, silver (Ag), aluminum (Al), nickel (Ni), an
aluminum-alumina composite material (aluminum-alumina composite
brazing), an alloy containing at least two of the following:
indium, gold, silver, aluminum, nickel, and titanium.
In particular, it is preferable that the bonding members 13 and 23
and the terminals 14 and 24 be bonded to each other by any of
indium, gold, silver, the aluminum-alumina composite material
(aluminum-alumina composite brazing), and a gold-nickel ally
(Au--Ni). According to this, the bonding members 13 and 23 and the
terminals 14 and 24 are firmly bonded to each other, and the
bonding of the terminals 14 and 24 to the electrodes 12 and the
resistance heating elements 22, both of which are bonded to each
other through the bonding members 13 and 23, can be made
firmer.
The brazing can be performed by interposing the brazing material
between the bonding members 13 and 23 and the terminals 14 and 24
and heating all the above at 130 to 1100.degree. C. Moreover, the
bonding members 13 and 23 may also have recessed portions into
which the terminals 14 and 24 are insertable. In this case, the
terminals 14 and 24 can be inserted into the recessed portions of
the bonding members 13 and 23, and can be thus bonded to the
bonding members 13 and 23.
Moreover, it is preferable that tensile strengths of the bases 11,
21 and 31 at breaking points thereof in the case of applying loads
to pull the bases 11, 21 and 31 and the terminals 14 and 24 in
directions separating from each other be 1.0 kg weight/mm.sup.2 or
more. According to this, the terminals 14 and 24 can be firmly
bonded to the electrodes 12 and the resistance heating elements 22.
More preferable tensile strengths are 1.4 kg weight/mm.sup.2 or
more.
Here, an example of a method of measuring such tensile strength of
each base at the breaking point thereof in the case of applying the
load to pull each base and each terminal in the reverse directions
is shown in FIG. 4. A description will be made with reference to
FIG. 4 by taking the electrostatic chuck 10 shown in FIG. 1, as an
example of the alumina member. The base 11 is fixed to a fixture 5
which includes a folded portion 5a for holding the base 11 and
fixes the base 11. The terminal 14 is grasped by a pulling jig 4
which grasps and pulls the terminal 14. The pulling jig 4 is
connected to an auto graph 3. The terminal 14 is pulled by using
the auto graph 3 through the pulling jig 4 so as to separate from
the base 11, that is, in a direction of an arrow A in FIG. 4, and
in such a way, such a tensile load to pull the base 11 and the
terminal 14 in the reverse directions is applied to both thereof.
The tensile strength of the base 11 at the breaking point thereof
is measured by the auto graph 3.
Moreover, it is preferable that a punching load to the base at the
breaking point thereof in the case of applying the load to the base
in a direction from the terminal toward the bonding member be 30 kg
weight or more. According to this, the strengths of the bases 11,
21 and 31 in the peripheries of bonded portions of the terminals 14
and 24 to the electrodes 12 and the resistance heating elements 22
can be increased, and the strengths of the entire alumina members
such as the electrostatic chucks 10 and 30 and the heater 20 can be
maintained high. A more preferable punching load is 40 kg weight or
more.
Here, an example of a method of measuring the punching load to the
base at the breaking point thereof in the case of applying the load
thereto in the direction from the terminal toward the bonding
member is shown in FIG. 5. A description will be made with
reference to FIG. 5 by taking the electrostatic chuck 10 shown in
FIG. 1, as an example of the alumina member. The base 11 is mounted
on a support jig 7 which includes a protruding portion 7a
supporting the base 11 while providing a space 8 between the base
11 and the support jig 7 and supports the base 11. By using the
auto graph 3, the load is applied through a push rod 6 to the
bonding member 13 from a position thereof where the terminal 14 is
to be provided, in a direction toward the bonding member 13
(direction of arrow B in FIG. 5). The push rod 6 and the autograph
3 are connected to each other. By the auto graph 3, the punching
load to the base 11 at the breaking point thereof is measured. As
described above, the load is applied to the base from the position
thereof where the terminal is to be provided, in the direction
toward the bonding member in a state where the terminal is not
provided, thus making it possible to measure the punching load.
Moreover, it is preferable that the withstand voltage of the
alumina member such as the electrostatic chucks 10 and 30 and the
heater 20 be stable at 3 kV/mm or more. According to this, the
arching can be prevented from occurring during use of the alumina
member.
Moreover, it is preferable that the base 11, the bonding member 13,
and the electrode 12 be an integral sintered body. It is preferable
that the base 21, the bonding members 23, and the resistance
heating element 22 be an integral sintered body. It is preferable
that the base 31, the bonding members 13 and 23, the electrode 12,
and the resistance heating element 22 be an integral sintered body.
According to these, the basses 11, 21 and 31, the bonding members
13 and 23, and the power-supplied members such as the electrodes 12
and the resistance heating elements 22 are bonded to one another
more firmly. In particular, it is preferable that each integral
sintered body be formed by the sintering using the hot
pressing.
The alumina members such as the electrostatic chucks 10 and 30 and
the heater 20 can be manufactured by a step of fabricating the
bases 11, 21 and 31 composed, for example, of the
alumina-containing sintered bodies, in which the differences in
coefficient of thermal expansion from the sintered bodies concerned
to the electrodes 12 and the resistance heating elements 22, which
are the power-supplied members, are 2.times.10.sup.-6/K or less,
and the bonding members 13 and 23 bonded to the electrodes 12 and
the resistance heating elements 22 are embedded, and a step of
bonding the terminals 14 and 24 to the bonding members 13 and
23.
A description will be made, as an example, of a manufacturing
method of the electrostatic chuck 10 and the heater 20. First,
alumina granulated powder is prepared. To material powder of the
alumina-containing sintered body, a binder, water, a dispersant,
and the like are added and mixed, and slurry is thus prepared. For
the material powder, there can be used only the alumina powder,
mixed powder of the alumina powder and zirconia powder, mixed
powder of the alumina powder and magnesia powder, and the like. The
obtained slurry is granulated by spray granulation, and the alumina
granulated powder is thus obtained.
Next, the alumina-containing sintered body is fabricated. The
obtained alumina granulated powder is molded by a molding method
such as die molding and cold isostatic pressing (CIP). A compact
thus obtained is sintered at 1500 to 1700.degree. C. by a sintering
method such as the hot pressing and normal pressure sintering in an
atmosphere of inert gas such as nitrogen gas and argon gas or an
oxidation atmosphere. More preferable sintering temperature is 1600
to 1700.degree. C.
Next, the power-supplied member such as the electrode 12 and the
resistance heating element 22 is formed on a sintered body thus
obtained. For example, the electrode 12 or the resistance heating
element 22 can be formed by being printed on the surface of the
sintered body by screen printing or the like. In this case, it is
preferable to mix the alumina powder in the print paste containing
the high melting point conductive material powder of tungsten,
niobium, molybdenum, an alloy of these, tungsten carbide, and the
like. According to this, adherence of the bases 11 and 21 to the
electrode 12 and the resistance heating element 22 can be enhanced.
Moreover, the electrode 12 can also be formed by mounting, on the
sintered body, the mesh-like bulk member (wire netting) of the high
melting point conductive material, the bulk member (punching metal)
of the high melting point conductive material, into which a large
number of holes is drilled, and the like. Moreover, the resistance
heating element 22 can also be formed by mounting, on the sintered
body, the coil-like or linear bulk member of the high melting point
conductive material, and the mesh-like bulk member (wire netting)
of the high melting point conductive material.
Next, the bonding member 13 and 23 are disposed in contact with the
power-supplied members such as the electrode 12 and the resistance
heating element 22. For example, by mounting the bonding member 13
on the electrode 12, the bonding member 13 can be disposed in
contact with the electrode 12. Moreover, by inserting the end of
the coil-like resistance heating element 22 into the through hole
23a of the bonding member 23, the bonding member 23 can be disposed
in contact with the resistance heating element 22. Note that, for
the bonding members 13 and 23, ones in which melting point is
higher than the baking temperature are used in the following
fabrication of the sintered body by the hot pressing. According to
this, in the manufacturing process, the bonding members 13 and 23
can be prevented from being deformed, and the component of the
bonding members can be prevented from being diffused into the bases
11 and 21.
Next, in a die mold, each of the sintered bodies, in which the
power-supplied members such as the electrode 12 and the resistance
heating element 22 are formed, and the bonding members 13 and 23
are disposed, is set. Then, the sintered body, the power-supplied
member, and the bonding member are filled with the prepared alumina
granulated powder, and the alumina-containing compact is thus
formed. Note that the compact may be formed separately, and mounted
on the sintered body, followed by press molding.
Then, the alumina-containing compacts, the power-supplied members
such as the electrode 12 and the resistance heating element 22, the
bonding members 13 and 23, and the alumina-containing sintered
bodies, are integrally sintered by the hot pressing, and the
integral sintered bodies are thus obtained. According to this, the
power supplied members such as the electrode 12 and the resistance
heating element 22 and the bonding members 13 and 23 can be
subjected to the thermal pressure bonding by the hot pressing.
Hence, the electrode 12 and the resistance heating element 22 which
are the power-supplied members and the bonding members 13 and 23
can be firmly bonded to each other, and the bonding of the
terminals 14 and 24 to the electrode 12 and the resistance heating
element 22, the bonding being formed through the bonding members 13
and 23, can be made firmer.
Specifically, the baking is performed at 1500 to 1700.degree. C. in
the atmosphere of inert gas such as nitrogen gas and argon gas or
the oxidation atmosphere while pressurization is being performed in
an axial direction. According to this, the power-supplied members
such as the electrode 12 and the resistance heating element 22 and
the bonding members 13 and 23 can be bonded to each other more
firmly. More preferable baking temperature is 1600 to 1700.degree.
C. Moreover, it is preferable that the pressure to be applied be 50
to 300 kg/cm.sup.2. According to this, the power-supplied members
such as the electrode 12 and the resistance heating element 22 and
the bonding members 13 and 23 can be bonded to each other more
firmly. More preferable pressure to be applied is 100 to 200
kg/cm.sup.2.
In the case of performing the baking in such a state where the
bonding member 13 and 23 are in contact with the alumina-containing
compacts as described above, it is preferable that the baking be
performed in a state where carbon is present in the periphery of
each of the bonding members 13 and 23. According to this, the
component of the bonding members can be prevented from being
diffused into the bases 11 and 21. In particular, though the
component of the bonding members is sometimes diffused into the
bases 11 and 21 when the bonding members 13 and 23 contain niobium,
such diffusion can be prevented by performing the baking in the
state where carbon is present in the peripheries of the bonding
members 13 and 23.
For example, the alumina-containing compacts contain the binder
serving as a carbon source as described above, thus making it
possible to perform the baking in the state where carbon is present
in the peripheries of the bonding members 13 and 23. Alternatively,
the alumina-containing compacts may contain carbon powder, or may
contain both of the binder and the carbon powder. Although the
binder is not limited as long as the binder turns to carbon by the
baking, for example, it is preferable to use, as the binder,
polyvinyl alcohol (PVA), stearic acid, and the like.
In this case, it is satisfactory if at least a part of each compact
contains at least one of either the carbon powder or the binder
serving as the carbon source. It is preferable that the compact
which turns to the dielectric layer 11a by the baking should not
contain the carbon powder or the binder. The compact which turns to
the sintered body composing the layer under the electrode 12 by the
baking may contain the carbon powder and the binder, or not.
In this case, it is preferable to adjust the content and baking
conditions of at least one of either the carbon powder or the
binder in the compact so that carbon contained in at least a part
of the sintered body of the base can be 0.05 to 0.5 wt %, that is,
so that an amount of residual carbon remaining in the sintered body
can be 0.05 to 0.5 wt %. According to this, a stronger alumina
member such as the electrostatic chuck 10 and the heater 20 can be
provided. For example, in the base 11, an adjustment can be
performed so that a portion other than the dielectric layer 11a,
that is, the sintered body composing the layer under the electrode
12 can contain 0.05 to 0.5 wt % carbon.
For example, in the case of fabricating the binder-containing
compact, the binder content can be set at 1 to 11 wt %. Moreover,
in the case of fabricating the carbon powder-containing compact,
the carbon content can be set at 0.05 to 0.5 wt %. Then, the baking
conditions such as the baking temperature, a holding time (baking
time) at the baking temperature, and a temperature rise rate are
adjusted, thus making it possible to adjust the amount of carbon
(residual amount of carbon) contained in the sintered body at 0.05
to 0.5 wt %. The baking temperature can be selected, for example,
from 1500 to 1700.degree. C. The baking time can be set, for
example, at 1 to 4 hours. The temperature rise rate can be set, for
example, so as to be 100 to 700.degree. C. per hour from room
temperature to approximately 1100.degree. C., and then to be 30 to
150.degree. C. per hour in a range of approximately 1400 to
1700.degree. C.
In the case of fabricating the compact which does not contain the
carbon powder or the binder, the bonding members 13 and 23 are
coated with carbon or the carbon sources, thus making it possible
to perform the baking in the state where carbon is present in the
peripheries of the bonding members 13 and 23. For example,
tape-like carbon and a tape-like carbon source which turns to
carbon by baking resin and the like can be pasted onto the bonding
members 13 and 23. Moreover, a solution or paste containing the
carbon or the carbon source can be sprayed to the bonding members
13 and 23 by using a spray and the like, can be coated on the
bonding members 13 and 23 by using a brush and the like, and so on.
Alternatively, the bonding members 13 and 23 may be immersed in the
solution or paste containing carbon and the carbon source, followed
by raising (dipping). As a solvent, for example, thinner and the
like can be used. It is preferable that thickness of carbon and the
carbon source, which cover the bonding members 13 and 23, be, for
example, approximately 50 to 200 .mu.m.
Next, the integral sintered bodies thus obtained are processed.
Specifically, the holes 15 and 25 are drilled in the bases 11 and
21. The holes 15 and 25 are drilled on the opposite surfaces of the
bases 11 and 21 to the substrate mounting surfaces 16 and 26. The
holes 15 and 25 are drilled to depth at which the bonding members
13 and 23 are exposed. Moreover, in the case of the electrostatic
chuck 10, it is preferable to grind the sintered body so that the
thickness of the dielectric layer 11a can be 0.2 to 0.5 mm.
Finally, the terminals 14 and 24 are bonded to the bonding members
13 and 23, and the terminals 14 and 24 are bonded to the
power-supplied members such as the electrode 12 and the resistance
heating element 22 through the bonding members 13 and 23. The
terminals 14 and 24 are inserted into the holes 15 and 25 drilled
in the bases 11 and 21, and are bonded to the exposed portions of
the bonding members 13 and 23. The bonding members 13 and 23 and
the terminals 14 and 24 are bonded to each other by the
brazing.
In the electrostatic chuck 30, the electrode 12 is formed on the
alumina-containing sintered body, the bonding member 13 is disposed
therebetween, the granulated granules are filled thereinto, and the
compact is thus fabricated on the sintered body. Moreover, the
resistance heating element 22 is formed on the fabricated compact,
the bonding members 23 are disposed therebetween, the granulated
granules are filled thereinto, and the compact is thus fabricated.
The electrostatic chuck 30 can be manufactured in a similar way to
the electrostatic chuck 10 and the heater 20 except the
above-described points.
Note that the power-supplied member is formed on the
alumina-containing compact, the bonding member is disposed
therebetween, and the alumina granulated powder is filled
thereonto, and in such a way, the compact in which the
power-supplied member and the bonding member are embedded may be
fabricated. Also in this case, the obtained compact can be
integrally baked by the hot pressing. As described above, when the
alumina-containing compact, the power-supplied member, and the
bonding member are integrally baked by the hot pressing, and the
power-supplied member and the bonding member are bonded to each
other, the entire portion which becomes each of the bases 11, 21
and 31 may be made as the alumina compact, and a part thereof may
be made as the alumina sintered body.
As described above, in accordance with the alumina members such as
the electrostatic chucks 10 and 30 and the heater 20 of this
embodiment, the terminals 14 and 24 are firmly bonded to the
power-supplied members such as the electrodes 12 and the heat
resistance elements 22 through the bonding members 13 and 23.
Moreover, the bases 11, 21 and 31 as the alumina-containing
sintered bodies and the bonding members 13 and 23 are approximate
to each other in coefficient of thermal expansion. Accordingly, the
cracks which may be caused by embedding the bonding members 13 and
23 into the bases 11, 21 and 31 can be prevented from occurring.
Hence, the strengths of the alumina members 10 and 30 and the
heater 20, which are the alumina members, can be enhanced by
embedding the bonding members 13 and 23 therein. In addition, the
cracks which may be caused by the embedding can also be prevented
from occurring. Therefore, the strength of each alumina member can
be increased. Moreover, the arcing which may be caused by the
cracks can be prevented from occurring. In addition, the melting
point of the bonding members 13 and 23 is higher than the baking
temperature of the sintered bodies. Accordingly, in the
manufacturing process of the alumina members, the bonding members
13 and 23 can be prevented from being deformed, and the component
of the bonding members can be prevented from being diffused into
the bases 11, 21 and 31. Hence, the malfunction does not occur
owing to the embedding of the bonding members 13 and 23.
Moreover, distances from the holes 15 and 25 for inserting the
terminals 14 and 24 thereinto, which are drilled in the bases 11,
21 and 31, to the substrate mounting surfaces 16, 26 and 36 can be
elongated by the lengths of the bonding members 13 and 23, and the
strengths of the electrostatic chucks 10 and 30 and the heater 20
can be enhanced. Hence, even in the Coulomb-type electrostatic
chucks 10 and 30 in each of which the thickness of the dielectric
layer 11a is thin, the strengths thereof are not reduced owing to
the formation of the holes 15 and 25. In addition, when the holes
15 and 25 are drilled in the bases 11, 21 and 31, the positions and
depths of the holes 15 and 25 can be determined by using the
bonding members 13 and 23, and processing accuracy can also be
enhanced.
EXAMPLES
Next, the present invention will be described more in detail by
examples; however, the present invention is not limited to the
following examples at all.
Examples 1 to 6, Comparative Examples 1 to 3
As ceramics material powder, alumina powder with a purity of 99.9
wt % and a mean particle diameter of 0.5 .mu.m was prepared. To the
alumina powder, water, the dispersant, and polyvinyl alcohol as the
binder were added, and were mixed by a trammel, and the slurry was
thus prepared. The obtained slurry was sprayed and dried by using a
spray dryer, and the alumina granulated powder was prepared. The
prepared alumina granulated powder was filled into the die mold,
and was pressurized with 200 kg/cm.sup.2, and nine compacts were
fabricated.
The obtained alumina compacts were set in a carbon-made sheath,
were baked by the hot pressing, and the alumina sintered bodies
were obtained. Specifically, the compacts were baked in a
nitrogen-pressurized atmosphere (nitrogen: 150 kPa) while being
pressurized with 100 kg/cm.sup.2. Moreover, the baking was
performed while raising the temperature from room temperature to
1600.degree. C. at a rate of 100.degree. C. per hour and
maintaining the temperature at 1600.degree. C. for two hours.
Next, ethylene cellulose was mixed as the binder into mixed powder
of 80 wt % tungsten (W) and 20 wt % alumina, and the print paste
was prepared. The electrode was formed on the alumina sintered body
by the screen printing, followed by drying. Next, bonding members
of Examples 1 to 6 and Comparative examples 2 and 3 were mounted on
the electrodes of eight sintered bodies.
Each alumina sintered body in which the electrode was formed and on
which the bonding member was mounted was set in the die mold. The
prepared alumina granulated powder was filled on the alumina
sintered body, the electrode, and the bonding member, and was
pressurized with 200 kg/cm.sup.2, and press molding was thus
performed therefor. Moreover, as Comparative example 1, the alumina
granulated granules were filled on the alumina sintered body and
the electrode without mounting the bonding member thereon, and the
press molding was thus performed therefor.
The integrally molded alumina sintered body, electrode, bonding
member, and alumina compact were set in the carbon-made sheath, and
were baked by the hot pressing. Specifically, the set objects were
baked in the nitrogen-pressurized atmosphere (nitrogen: 150 kPa)
while being pressurized with 100 kg/cm.sup.2, and the bonding
member and the electrode were bonded to each other. Moreover, the
baking was performed while raising the temperature from room
temperature to 1600.degree. C. at a rate of 100.degree. C. per hour
and maintaining the temperature at 1600.degree. C. for two
hours.
The integral sintered body thus obtained was processed into a disc
shape with a diameter of 340 mm and a thickness of 5 mm, and a hole
for attaching the terminal thereinto was drilled. The hole was
processed so that a diameter thereof could be 6 mm and a distance
from the substrate mounting surface to the hole could be 0.4 mm.
Moreover, the integral sintered body was ground so that thickness
from the base surface of the alumina sintered body to the electrode
could be 0.3 mm. Then, the bonding member and the molybdenum
terminal were brazed by using indium as the brazing material while
being heated at 150.degree. C., and the electrode and the terminal
were bonded to each other through the bonding member. In such a
way, the alumina members of Examples 1 to 6 and Comparative
examples 2 and 3 were fabricated. Moreover, the electrode and the
terminal were directly bonded to each other, and the alumina member
of Comparative example 1 was fabricated.
Niobium was used as the material of the bonding members of Examples
1 to 5. Moreover, the bonding members of Examples 1 to 5 were
formed into disc shapes with the following diameters and
thicknesses: a diameter of 3.0 mm and a thickness of 1.0 mm in
Example 1; a diameter of 3.0 mm and a thickness of 0.5 mm in
Example 2; a diameter of 3.0 mm and a thickness of 0.2 mm in
Example 3; a diameter of 2.0 mm and a thickness of 0.5 mm in
Example 4; and a diameter of 2.0 mm and a thickness of 0.2 mm in
Example 5. The bonding member of Example 6 was formed of platinum
(pt) as the material into a disc shape with a diameter of 3.0 mm
and a thickness of 1.0 mm.
The bonding member of Comparative example 2 was formed of
molybdenum (Mo) as the material into a disc shape with a diameter
of 3.0 mm and a thickness of 1.0 mm. The bonding member of
Comparative example 3 was made as a compact with 60 wt % tungsten
(W) and 40 wt % alumina (Al.sub.2O.sub.3). For the bonding member
of Comparative example 3, a compact in a disc shape with a diameter
of 3.0 mm and a thickness of 1.0 mm was fabricated by the die
molding.
The coefficient of thermal expansion of the alumina sintered body
composing the base of the obtained alumina member and the
coefficient of thermal expansion of the bonding member were
measured by a differential dilatometer (TM8310 made by Rigaku
Corporation), and the difference in coefficient of thermal
expansion between both thereof was obtained. Moreover, the surface
and longitudinal cross section of the alumina member was observed
by a scanning electron microscope (SEM), and it was confirmed
whether or not the crack occurred and the component of the bonding
member was diffused into the base of the alumina sintered body.
Moreover, the load to pull the base and the terminal in the
directions separating from each other was applied thereto by the
measurement method shown in FIG. 4, the tensile strength of the
base at the breaking point thereof was measured, and the strength
of the bonding of the electrode and the terminal was evaluated.
Note that a pulling rate was set at 0.5 mm per minute. Moreover,
the load was applied to the base in the direction from the terminal
toward the bonding member by the measurement method shown in FIG.
5, the punching load to the base at the breaking point thereof was
measured, and the strength of the alumina member was evaluated.
Note that a loading rate was set at 0.5 mm per minute, and the push
rod 6 with a diameter of 2 mm was used. Moreover, the measurement
was performed before attaching the terminal to the base.
Furthermore, withstand voltage characteristics of the bonded body
in which the terminal, the bonding member, and the electrode were
bonded to one another were evaluated by applying a voltage of 3 kV
to the terminal and confirming whether or not the arcing occurred.
Results are shown in Table 1.
TABLE-US-00001 TABLE 1 Difference in coefficient of thermal Tensile
expansion strength Punching load Withstand voltage Bonding member
(/K) Crack Diffusion (kg wt/mm.sup.2) (kg wt) characteristics
Example 1 Nb: 1.3 .times. 10.sup.-6 None None 1.4 69 Arcing did not
O 3.0 mm .times. occur t 1.0 mm Example 2 Nb: 1.3 .times. 10.sup.-6
None None 1.4 46 Arcing did not O 3.0 mm .times. occur t 0.5 mm
Example 3 Nb: 1.3 .times. 10.sup.-6 None None 1.4 35 Arcing did not
O 3.0 mm .times. occur t 0.2 mm Example 4 Nb: 1.3 .times. 10.sup.-6
None None 1.0 44 Arcing did not O 2.0 mm .times. occur t 0.5 mm
Example 5 Nb: 1.3 .times. 10.sup.-6 None None 1.0 34 Arcing did not
O 2.0 mm .times. occur t 0.2 mm Example 6 Pt: 0.6 .times. 10.sup.-6
None None 1.4 57 Arcing did not O 3.0 mm .times. occur t 1.0 mm
Comparative -- Present -- 0.2 21 Arcing occurred Example 1
Comparative Mo: 3 .times. 10.sup.-6 Present None 0.8 21 Arcing
occurred Example 2 O 3.0 mm .times. t 1.0 mm Comparative W +
Al.sub.2O.sub.3: 1.4 .times. 10.sup.-6 Present None 0.8 20 Arcing
occurred Example 3 O 3.0 mm .times. t 1.0 mm
As shown in Table 1, in the alumina members of Examples 1 to 5, in
each of which the electrode and the terminal were bonded to each
other through the niobium-made bonding member, and of Example 6 in
which the electrode and the terminal were bonded to each other
through the platinum-made bonding member, the tensile strengths
were as high as 1.0 kg weight/mm.sup.2 or more, and the electrodes
and the terminals were firmly bonded to each other.
Moreover, each alumina member of Examples 1 to 6 had the punching
load of 30 kg weight or more, and had higher strength than that of
Comparative example 1 equivalent to the conventional alumina member
which does not include the bonding member. As described above, in
Examples 1 to 6, the bonding members were provided, and in such a
way, even if the holes for inserting the terminals thereinto were
drilled, the strengths of the bases in the peripheries of the
bonded portions of the electrodes and the terminals were high, and
the strengths of the alumina members were maintained high. In
particular, in the alumina members of Examples 2 and 4 in each of
which the thickness of the bonding member was 0.5 mm, the punching
loads were 40 kg weight or more, and in the alumina members of
Examples 1 and 6 in each of which the thickness of the bonding
member was 1.0 mm, the punching loads were 55 kg weight or more,
and the strengths were high.
Moreover, in each alumina member of Examples 1 to 5, the difference
in coefficient of thermal expansion between the base and the
bonding member was 1.3.times.10.sup.-6/K. In the alumina member of
Example 6, the difference in coefficient of thermal expansion
between the base and the bonding member was 0.6.times.10.sup.-6/K.
No crack occurred in the bases of the alumina sintered bodies of
Examples 1 to 6. Accordingly, when the punching loads in Examples 1
and 6 and the punching loads in Comparative examples 2 and 3,
between which the thicknesses of the bonding members were the same,
are compared with each other, the alumina members in Examples 1 and
6 free from the crack had the strengths approximately three times
those of the alumina members in Comparative examples 2 and 3 in
which the cracks occurred. Hence, it was found that the base and
the bonding member are approximated to each other in coefficient of
thermal expansion so that the difference therebetween can be
2.times.10.sup.-6 or less, thus making it possible to prevent the
crack from occurring, thereby making it possible to enhance the
strength of each alumina member. Moreover, in each alumina member
of Examples 1 to 6 free from the crack, the arcing did not occur,
and the alumina member was excellent in withstand voltage
characteristics.
Moreover, the melting point of the bonding members of Examples 1 to
5 is 2470.degree. C., and the melting point of the bonding member
of Example 6 is 1770.degree. C. Both of the melting points are
higher than the baking temperature of 1600.degree. C. by
150.degree. C. or more. Accordingly, each bonding member was not
deformed either. Furthermore, each component of the boding members
of Examples 1 to 6 was not diffused into the base.
In comparison with the alumina members of Examples 1 to 6, in each
of the alumina member of Comparative example 1 in which the
electrode and the terminal are directly bonded to each other
without providing the bonding member, the alumina member of
Comparative example 2 using the molybdenum-made bonding member, and
the alumina member of Comparative example 3 using, as the bonding
member, the compact of tungsten and alumina, the tensile strength
was weak, and the bonding was weak.
Moreover, in the alumina member of Comparative example 1 in which
the bonding member is not provided, the punching load was also
extremely low, and the strength was low. Furthermore, in each
alumina member of Comparative examples 2, the crack occurred in the
base of the alumina sintered body owing to the difference in
coefficient of thermal expansion between the electrode and the base
and owing to the difference in coefficient of thermal expansion
between the bonding member and the base. In the alumina member of
Comparative example 3, though the crack did not occur immediately
after the baking, the crack occurred in the alumina member after
being processed for observing the cross section thereof. It is
considered that this is because a residual stress was high, a
residual stress was released by the processing, and the base was
thereby broken. In each alumina member of Comparative examples 2
and 3, since the crack occurred, the punching load thereof was
approximate one-third or less of those in Examples 1 and 6 in each
of which the bonding member with the same thickness was provided,
and the strength could not be maintained. Moreover, in each alumina
member of Comparative examples 1 to 3, the arcing occurred owing to
the crack, and the alumina member was also inferior in withstand
voltage characteristics.
Examples 7 to 9
In Example 7, an alumina member in which the niobium-made bonding
member was embedded was fabricated in a similar way to Example 1
except that polyvinyl alcohol as the binder was not added thereto.
In Example 8, an alumina member on which the carbon tape was coated
and in which the niobium-made bonding member was embedded was
fabricated in a similar way to Example 7 except that the tape-like
carbon (carbon tape) with a thickness of approximately 0.1 mm was
pasted to the bonding member, and that the bonding member was
coated with carbon. In Example 9, an alumina member in which the
platinum-made bonding member was embedded was fabricated in a
similar way to Example 6 except that polyvinyl alcohol as the
binder was not added thereto.
For each of the alumina members of Examples 7 and 9, in a similar
way to Example 1, it was confirmed whether or not the crack
occurred and the component of the bonding member was diffused into
the base of the alumina sintered body, and the punching load was
measured. Moreover, by high frequency heating infrared
absorptiometry, the amount of carbon contained in each alumina
sintered body was measured. For each of Examples 1 and 6, the
amount of carbon was measured. Results in Examples 1 and 6 to 9 are
shown in Table 2.
TABLE-US-00002 TABLE 2 Amount of Presence of carbon Punching load
Bonding member carbon Crack Diffusion (wt %) (kg wt) Example 1 Nb:
binder is None None 1.4 69 O 3.0 mm .times. present t 1.0 mm
Example 7 Nb: binder is not None Present: 0 35 O 3.0 mm .times.
present 200 .mu.m t 1.0 mm Example 8 Nb: binder is not None
Present: 0 46 O 3.0 mm .times. present/ 100 .mu.m or t 1.0 mm
carbon tape is less present Example 6 Pt: binder is None None 1.5
57 O 3.0 mm .times. present t 1.0 mm Example 9 Pt: binder is not
None None 0 49 O 3.0 mm .times. present t 1.0 mm
As shown in Table 2, the cracks did not occur in Examples 7 to 9,
either. Moreover, in Example 7 in which the niobium-made bonding
member was used, the binder was not added, and the bonding member
was not covered with the carbon tape, either, the diffusion of the
component of the bonding member into the base was confirmed, and a
diffusion layer with a thickness of 200 .mu.m was formed in the
periphery of the bonding member. As opposed to this, in Example 1
in which the binder was added even in the case of using the
niobium-made bonding member, the diffusion of the component of the
bonding member into the base was not observed at all. Moreover, in
Example 8 in which the niobium-made bonding member was used, and
the bonding member was covered with the carbon tape, though the
diffusion of the component of the bonding member into the base was
confirmed, the thickness of the diffusion layer was controlled to
100 .mu.m or less. Specifically, in Example 8, the diffusion was
extremely little, and the extent of the diffusion was improved to a
great extent as compared with Example 7. Hence, it was able to be
confirmed that the diffusion of the component of the bonding member
into the base was able to be prevented by performing the baking in
the state where carbon was present in the periphery of the bonding
member.
Moreover, in the case of using the platinum-made bonding member,
both in Example 6 in which the binder was added and in Example 9 in
which the binder was not added, the diffusion of the component of
the bonding member into the base was not observed at all. Hence, it
was able to be confirmed that the diffusion of the component of the
bonding member into the base was able to be prevented when the
bonding member contained platinum.
Furthermore, in each of Examples 1 and 6 in each of which the
amount of carbon contained in the alumina sintered body was 1.4 to
1.5 wt %, the punching load was higher than in Examples 7 to 9 in
which carbon was not contained. Hence, it was able to be confirmed
that the strength of the alumina member was able to be further
improved in such a manner that the alumina member contained 0.05 to
0.5 wt % carbon.
Example 10
Alumina granulated powder was prepared in a similar way to Example
1. The prepared alumina granulated powder was filled into the die
mold, and was pressurized with 200 kg/cm.sup.2. While an alumina
compact thus obtained was being set in the die mold, a mesh-like
niobium-made electrode (line diameter: o 0.12 mm; mesh: # 50 .mu.m)
was mounted on the alumina compact. Moreover, a disc-like
niobium-made bonding member with a diameter of 3.0 mm and a
thickness of 1.0 mm was mounted on the electrode.
The alumina granulated powder was filled onto the alumina compact,
the electrode, and the bonding member, and was pressurized with 200
kg/cm.sup.2, and the press molding was performed therefor. A
coil-like niobium-made resistance heating element (line diameter: o
0.5 mm; winding diameter: o 3.0 mm) was mounted on the obtained
alumina compact. Moreover, an end of the resistance heating element
was inserted into a through hole of a ball-like niobium-made
bonding member with a diameter of 4.0 mm, and the niobium-made
bonding member was also mounted on the compact. The alumina
granulated powder was filled onto the alumina compact, the
resistance heating element, and the bonding member, and was
pressurized with 200 kg/cm.sup.2, and the press molding was
performed therefor.
The obtained compact in which the electrode, the resistance heating
element, and the bonding member were embedded was set in the
carbon-made sheath, and was baked by the hot pressing.
Specifically, the compact was baked in a nitrogen-pressurized
atmosphere (nitrogen: 150 kPa) while being pressurized with 100
kg/cm.sup.2. In such a way, the bonding member and the electrode
were bonded to each other, and the bonding member and the
resistance heating element were bonded to each other. Moreover, the
above-described members were integrally baked while raising the
temperature from room temperature to 1600.degree. C. at a rate of
100.degree. C. per hour and maintaining the temperature at
1600.degree. C. for two hours.
An integral sintered body thus obtained was processed into a disc
shape with a diameter of 330 mm and a thickness of 15 mm, and a
hole for attaching the molybdenum-made terminal thereinto was
formed therein. Then, the bonding member and the terminal were
brazed to each other, the electrode and the terminal were bonded to
each other through the bonding member, and the heat resistance
element and the terminal were bonded to each other through the
bonding member. The brazing was performed by using indium as the
brazing material and performing the heating at 150.degree. C. In
such a way, as the alumina member, an electrostatic chuck
subjectable to the heat treatment was fabricated.
When the obtained electrostatic chuck was observed by the SEM, the
occurrence of the crack was not observed. Moreover, when the
tensile strength and punching load of the electrostatic chuck was
measured in a similar way to Example 1, both tensile strengths of
the electrode portion and the resistance heating element portion
were 1.4 kg weight/mm.sup.2 or more, and the electrode portion and
the heat resistance element portion were firmly bonded to each
other. Moreover, the punching load of the electrode portion was 69
kg weight, the punching load of the resistance heating element
portion was 70 kg weight or more, and the electrostatic chuck had
high strength.
Moreover, a function as the electrostatic chuck was evaluated by
applying a voltage of 2 kV thereto. By applying the voltage to the
electrostatic chuck, the electrostatic chuck exerted absorbing
power of 40 Torr. Moreover, leak current was 1 nA or less,
responsiveness to attaching/detaching of the electrostatic chuck
was 1 second or less, and volume resistivity of the dielectric
layer at room temperature was 1.times.10.sup.15 Ocm or more. The
electrostatic chuck exerted electrostatic absorbing power (Coulomb
force) up to 200.degree. C. As described above, the alumina member
was excellent in absorbing power and responsiveness to
attaching/detaching thereof, and had excellent characteristics as
the electrostatic chuck.
Moreover, a function as the heater was evaluated by measuring heat
uniformity of the substrate mounting surface by a thermoviewer. A
temperature difference within the substrate mounting surface when
the temperature of the surface was set at 200.degree. C. was
10.degree. C. or less. As described above, the alumina member was
excellent in heat uniformity, and had excellent characteristics
also as the heater.
* * * * *